This pilot research grant proposal focuses on research objective 2: Cardiovascular and Cerebrovascular Aging. Aging is associated with increased oxidative stress and mitochondrial dysfunction in numerous tissues. These factors are thought to play a role in aging-associated decreases in ventricular function, coronary vascular reserve, and tolerance to myocardial ischemia-reperfusion all of which may contribute to the increase in cardiovascular disease with aging. Significant evidence has accumulated that mitochondria, in addition to maintaining the energy stores for the high work demands of ventricular myocardium, play a role in determining the cell's transition from reversible injury to apoptosis and necrosis. However there have been limited studies of ischemia-reperfusion injury in in vivo aged myocardium and few systematic investigations of mitochondrial function in intact ventricular myocytes of aged animals. This proposal will test the hypothesis that aged myocardittm exhibits less tolerance to ischemia-reperfusion injury and oxidative stress in part due to altered nitric oxide (NO) metabolism and signaling. Specific Aim 1 will determine whether in vivo myocardium and isolated ventricular myocytes from aged rats exhibit less tolerance to ischemia-reperfusion and hypoxia-reoxygenation, respectively. Specific Aim 2 will test the hypothesis that aging associated oxidative stress and mitochondrial dysfunction is due to increased formation of reactive nitrogen species. In Aim 1 studies adult (6 month) and aged (24 month) Fischer 344 x Brown Norway F1 hybrid (F344xBN) rats will be submitted to in vivo coronary artery occlusion and reperfusion and infarct size will be measured. Left ventricular myocytes isolated from adult and aged rats will be submitted to hypoxia-reoxygenation and twitch amplitude and intracellular oxidative stress will be measured. In Aim 2 studies isolated ventricular myocytes will be exposed to/-/202 tO induce oxidative stress. Mitochondrial ([Ca2+]), mitochondrial redox state, and intracellular oxidative stress will be measured under baseline conditions and during and following exposure to H202. The role of NO in modulating aged myocyte response to oxidative stress will be determined by modulating NOS activity and arginine levels and with a NO donor. The expression and subcellular compartmentation of anti-oxidant enzymes and NOS isoforms will be determined by Western blotting of subcellular fractions. The proposed studies will provide significant insight into the role of acute and chronic oxidative stress in aged myocardium and its modulation by NO. The results obtained may lead to the development of new therapies for treating cardiovascular disease in the elderly.